1. Field of the Invention
The present invention relates to a liquid crystal display device having a liquid crystal panel and, particularly, to a liquid crystal projector which projects an image of the liquid crystal panel. More specifically, the present invention relates to an improvement in a cooling structure for improving a heat resistant reliability.
2. Description of Related Art
A liquid crystal projector has been mainly used as a so-called home theater system for enjoying various movies at a home. In these days, a projection image quality has been improved by a high definition of liquid crystal panel and a high luminance brightness of lamp. Accordingly, the liquid crystal projector has been also used as a presentation system for projecting a display image of a personal computer on a projection screen.
A construction of the liquid crystal-projector is shown in FIG. 1. Light generated from a light source 1 of a high luminance lamp such as a metal-halide lamp, a xenon lamp or a UHP or the like, is reflected by a spherical reflecting mirror 2. Then, light reflected by the spherical reflecting mirror 2 transmits through a filter 3 so that unnecessary infrared ray and ultraviolet ray are removed. Further, light transmitting through the filter 3 transmits through an integrator lens 4 and a condenser lens 5 so as to be condensed, and thereafter, passes through an incidence side polarizing plate 6, and thus, is incident upon a liquid crystal panel 8. Light emitted from the liquid crystal panel 8 transmits through an emission side polarizing plate 7, and thereafter, is enlarged and projected by means of a projection lens 9, and thus, an image is projected onto a screen or the like located ahead of the projector.
The aforesaid structure is of a single-panel type using a sheet of liquid crystal panel including color filters. In addition to the above single-panel type structure, a three-panel type structure is also known such that light from a light source is decomposed into decomposition lights of three primary colors of RGB, and these decomposition lights are incident upon three liquid crystal panels.
A construction of the liquid crystal projector having the above three-panel type structure is shown in FIG. 2. In FIG. 2, like reference numerals used in the case of FIG. 1 are used to designate components having the same function as components shown in FIG. 1. In the construction shown in FIG. 2, the following components are used; more specifically, dichroic mirrors 10 for transmitting or reflecting an incident light in accordance with a wavelength, a complex prism 11 for synthesizing light, and total reflection mirrors 12. Light, which is generated from the light source 1 and reflected by the spherical reflecting mirror 2, transmits through the filter 3 and the integrator lens 4, and thereafter, is guided to the dichroic mirrors 10 after its optical path is bent by one of the total reflection mirrors 12. Then, light from the light source 1 is decomposed into three primary color lights of red (R), green (G) and blue (B) by means of two dichroic mirrors 10 for reflecting or transmitting light having different wavelength band. Then, these decomposition lights are transmitted through the liquid crystal panel 8 corresponding to each of three primary colors, and thereafter, are synthesized by the complex prism 11, and thus, are projected.
In these liquid crystal projectors, there is a tendency for a projected image to be short of a brightness. The first factor is light absorption by polarizers 6 and 7 located front and rear the liquid crystal panel 8. The second factor is that the liquid crystal panel 8 has an area made small up to a size of about 1 inch in order to miniaturize the liquid crystal projector. More specifically, in the case where an image of the liquid crystal panel 8 having a small area is enlarged and projected to several tens of inches to several hundreds of inches, there is the case where the projected image is short of a brightness.
In order to solve these problems as described above, high output lamps such as high-luminance metal-halide lamp, Ultra High Pressure Mercury lamp and xenon lamp are used as the light source 1. However, in particular, in the presentation system, demands for further miniaturization, high definition and high luminance are made in the market and a higher output lamp is selected.
For this reason, in the liquid crystal projector system, a disadvantage by a heat is a significant problem.
For example, in general, an iodine-based polarizer is used as the polarizer constituting a liquid crystal display section. However, the iodine-based polarizer is not sufficient in light resistance, heat resistance and damp and heat resistance. For this reason, in particular, in the liquid crystal projector, a dye-based polarizer is used because of being excellent in light resistance, a heat resistance and a damp and heat resistance (see Unexamined Patent Publications (Kokai) No. 9-22008 and 9-22009)
However, in particular, the incidence side polarizer 6 has light transmittance of about 40%, and absorbs most of lights. Further, the polarizer 6 can not maintain its characteristic when becoming a temperature of 70xc2x0 C. or higher.
Moreover, the liquid crystal panel 8 itself is weak in a heat, and its characteristic is remarkably deteriorated when becoming a temperature of 60xc2x0 C. or higher.
In order to solve the above problem, in the liquid crystal projector, the following various cooling systems have been proposed.
(1) Air cooling system
Heat generating sections such as the incidence side polarizer 6, the liquid crystal panel 8 and the emission side polarizer 7, the light source 1 and a power source section, are cooled by means of a cooling fan, and then, an air having a heat is exhausted.
However, according to this air cooling system, there are a noise problem and a problem that a dust adheres to the liquid crystal panel 8. More specifically, in the case where an air supply is increased in order to obtain sufficient cooling effect, a fan is rotated at a high speed, and is made into a large size, and thereby, a large noise is generated. For this reason, it is not preferable to apply the above air cooling system to a liquid crystal projector which is used for conducting a presentation in a silent room or for enjoying a movie or the like.
(2) As shown in FIG. 1, the incidence side polarizer 6 is arranged in a state of separating from the liquid crystal panel 8 with a distance of about 1 to 5 mm. By doing so, it is possible to prevent a heat of the polarizer 6 from conducting directly to the liquid crystal panel 8. Further, a cooling air flows between the polarizer 6 and the liquid crystal panel 8, and thereby, a cooling efficiency can be enhanced.
In this system, the incidence side polarizer 6, which is a principal heat generating source, is arranged separately and independently, and thereby, an influence to the liquid crystal panel 8 is reduced, and a heat radiating effect can be improved. However, there is a limit in the cooling effect. Moreover, a blue sheet glass or white sheet glass is used as a retaining plate of a polarizing substance in the polarizer 6. In the blue or white sheet glass, the heat conductivity is worse and a heat radiating effect is insufficient. Therefore, like the case of the above air cooling system, finally, an output of the cooling fan must increased. As a result, it is impossible to solve the above problems relating a noise and dust adhesion.
(3) A heat radiating glass plate having a heat conductivity of 1 W/mxc2x7K or more is located on an outer surface of the liquid crystal panel 8 with a sealed space interposed therebetween, so as to enhance a heat radiating effect with respect to a heat generation of the liquid crystal panel 8. Further, a cooling air is supplied to the heat radiating glass plate so as to prevent a dust from adhering to the liquid crystal panel 8.
According to the above system, no dust adheres to the outer surface of the liquid crystal panel 8. Since a surface of the heat radiating glass plate diverges from a focal plane, even if a dust adheres to the surface of the heat radiating glass plate, the image of the dust is not imaged on a projection screen, and no influence is given to a projection image. However, a heat conductivity is 2 W/mxc2x7K or less at most even though the glass plate has a high heat conductivity and, therefore, sufficient heat radiating effect can not be obtained.
(4) Liquid cooling system
A liquid is encapsulated as a heat exchange medium in a space formed by a transparent panel arranged along the outer surface of the liquid crystal panel, and thus, a cooling effect is enhanced (see Examined Patent Publication (Kokoku) No. 6-58474).
According to the above liquid cooling system, with a temperature rise, there is the possibility that a pressure reduction is required, or a bubble is generated. Moreover, there is the possibility that a foreign matter gets mixed in the liquid used as a cooling medium, or the cooling medium leaks. For these reasons, in the liquid cooling system, the reliability is worse. In addition, the liquid is used and, therefore, the cooling system is a large scale as a whole. As a result, there is a problem that the whole of liquid crystal projector is made into a large size.
(5) Electronic cooling system using a Peltier element (solid cooling system)
An electronic cooling system with a Peltier element is attached to a heat generating source so as to forcedly cool the heat generating source.
According to such electronic cooling system, equipments for the electronic cooling system are required and there is a problem that the cost spent for the whole liquid crystal project or is greatly increased. In addition, a sufficient cooling effect can not be obtained.
(6) A polarized light converter is arranged just after a light source
Before light from the light source 1 is incident upon the polarizer 6, a polarizing direction is aligned with a transmission polarization axis of the polarizer 6 so as to reduce a quantity of light absorbed into the polarizer 6.
However, in this case, since about 20% of light incident upon the polarizer 6 is absorbed by the polarizer 6, there is the case where a sufficient cooling effect is not always obtained. More specifically, for example, the liquid crystal panel 8 is made into a small size, and the lamp intensity per unit area becomes higher, and thereby, there is the case where a sufficient cooling effect is not obtained.
As seen from the above description, even if the aforesaid conventional cooling systems are employed, a sufficient cooling effect can not be obtained with a simple structure.
The problem of generating a heat raises in various portions other than the polarizer 6.
For example, a pixel electrode and a switching element are formed on an incidence side transparent substrate which is a constituent element of the liquid crystal panel 8. At present, the transparent substrate is constructed with the use of a silica glass substrate having a low heat conductivity of about 1 or 2 W/mxc2x7K. For this reason, it is impossible to effectively release a heat accumulated in the liquid crystal panel 8.
Recently, a panel size is made small, and thereby, light quantity per unit area increases. In addition, in order to improve an aperture ratio, a micro lens is used so that an incident light is condensed and transmitted for each pixel. Thus, as seen from the above explanation, a thermal load acting on the liquid crystal panel itself becomes greater.
In a driving circuit, its operating speed is slow because in a liquid crystal display unit using a polysilicon thin-film transistor as conventionally, a mobility of polysilicon is slow. In addition, since a leakage current is large due to a fault of polysilicon, there is a problem that power consumption is much.
On the other hand, in the liquid crystal projector having the construction as shown in FIG. 2, the dichroic mirrors 10 are used. The dichroic mirrors 10 are manufactured in a manner of coating a thin film, which selects a wavelength of the light and carries out transmission/reflection, on the surface of a blue sheet glass or white sheet glass. The dichroic mirrors 10 also cause a heat generation by light absorption and, therefore, the temperature of apparatus rises up as a whole.
Moreover, there is the case where an infrared ray is previously cut from light incident upon an optical system from the light source 1 so as to restrict a heat generation. The blue sheet glass or white sheet glass is used as the filter 3 (see FIG. 2) for cutting an infrared ray. Since these sheet glasses have low heat conductivity, a heat is accumulated. As a result, this is a factor of a temperature rise in the whole of apparatus.
Meanwhile, since the single light source 1 is used, the integrator lens 4 is used in order to diffuse a light source intensity and make uniform illuminance of an irradiation surface. In general, the integrator lens 4 has the following structure; more specifically, an optical glass such as Pyrex glass is subjected to mold pressing, and many lenses thus manufactured are made into a single plate. Further, in order to improve a characteristic, there is the case where a material such as silica glass is used, and a total reflection of the side plane of a prism made of silica glass is utilized. In this case, the silica glass has a low refractive index of about 1.46 and, therefore, the total reflection angle becomes large. As a result, a length of the prism rod must be set longer. Moreover, there is a problem that the number of pseudo light sources is small.
It is, therefore, an object of the present invention to provide a liquid crystal display apparatus which includes a simple and effective cooling structure.
Another object of the present invention is to provide a projection type liquid crystal display apparatus (liquid crystal projector) which includes a simple and effective cooling structure.
Still another object of the present invention is to provide a liquid crystal display apparatus which has a fast operating speed, low power consumption and excellent radiation property, and is adaptable to miniaturization and high definition.
The present invention provides a liquid crystal display device, which includes a liquid crystal panel as one of optical components for transmitting, absorbing or reflecting light, any one of the optical components being comprised of a sapphire substrate.
According to one embodiment of the present invention, the liquid crystal display device further includes a light source, and the optical components transmits and projects light from the light source, thereby constructing a projection type display device.
More specifically, the optical components may further include a lens, and a polarizer having a polarizer film and a retaining plate for retaining the polarizer film, and the liquid crystal panel includes a transparent substrate, and further, any one of the lens, the retaining plate and the transparent substrate is comprised of a sapphire substrate, and thus, light from the light source may be transmitted through the lens, the polarizer and the liquid crystal panel so as to be projected.
Further, the optical components may further include a wavelength selective optical component for transmitting or reflecting light having a specific wavelength band, a lens, and a polarizer having a polarizer film and a retaining plate for retaining the polarizer film, and the liquid crystal panel includes a transparent substrate. Any one of the wavelength selective optical component, the lens, the retaining plate and the transparent substrate may be comprised of a sapphire substrate, and light from the light source may be transmitted through the lens, the polarizer and the liquid crystal panel so as to be projected.
In this case, the wavelength selective optical component may be a filter (for example, an infrared cut filter or an ultraviolet ray cut filter).
Moreover, the wavelength selective optical component may be a dichroic mirror.
With the above construction, the sapphire substrate having a high heat conductivity is used as a transparent substrate in the liquid crystal projector, and thereby, a heat radiating effect can be enhanced. More specifically, sapphire, which is excellent in heat conductivity, is used as various components of the liquid crystal display device, and thereby, a heat radiating effect can be improved. Therefore, it is possible to realize a high-luminance and small-size liquid crystal projector without causing a problem of characteristic deterioration by a heat generation.
Further, a metallic radiation fin may be bonded to the sapphire substrate, and thereby, a heat radiating effect can be improved more.
The transparent substrate of the liquid crystal panel may perform a function as the retaining plate of the polarizer film. More specifically, the polarizer film may be supported onto the surface of the transparent substrate of the liquid crystal panel.
Preferably, the sapphire substrate is constructed in a manner that an angle made by a C-axis direction or C-axis projection line direction and a polarized light transmission axis is set within a range of xc2x12xc2x0, or an angle made by an axis perpendicular to the C-axis and a polarized light transmission axis is set within a range of xc2x12xc2x0, or an angle made by a C-plane and a plane vertical to a transmission direction of a polarized light to be transmitted is set within a range of xc2x12xc2x0.
Whereby it is possible to prevent an influence to polarizing characteristic.
The lens may be an rod-type integrator lens for diffusing light from the light source, and the integrator lens may be formed of sapphire. More specifically, the sapphire has a high refractive index, so that it is possible to make small a total reflection angle, and to improve a diffusion of light from the light source.
A transparent adhesive agent having a Shore hardness of 30 or less may be applied onto the polarizer film or the liquid crystal panel so as to form a thickness of 10 to 70 xcexcm, and then, the sapphire substrate may be aligned and bonded thereto. Whereby it is possible to prevent a deformation of the liquid crystal panel generated by a difference of thermal expansion, and thereby, to reduce an influence to an image while preventing a failure in a heat conductivity
The sapphire substrate may be attached onto an outer surface of the liquid crystal panel so as to be sealed with a space of 0.1 mm or less interposed therebetween. Whereby the sapphire has no influence to the liquid crystal panel, and a generated heat is effectively conducted via a micro space, and thus, a cooling effect can be enhanced.
Further, in the case of attaching the sapphire substrate is attached onto an outer surface of the liquid crystal panel, preferably, light shielding layer having a window of a size larger by 0.1 mm or more than an effective pixel area of the liquid crystal panel is applied to the sapphire substrate. Whereby it is possible to prevent a projected image from receiving an influence of scattering light from the surroundings.
The liquid crystal panel may include a first transparent substrate and a second transparent substrate facing each other with a liquid crystal layer sandwiched therebetween. In this case, it is preferable that at least one of the first transparent substrate and the second transparent substrate is comprised of a sapphire substrate.
Further, the liquid crystal panel may include a first sapphire substrate and a second sapphire substrate used as a pair of transparent substrates facing each other with a liquid crystal layer sandwiched therebetween.
In this case, preferably, the first sapphire substrate whose primary plane is any one of an R-plane, an A-plane, an M-plane and a C-plane, and the second sapphire substrate whose primary plane is any one of an R-plane, an A-plane, an M-plane and a C-plane. Further, preferably, the first sapphire substrate and the second sapphire substrate face each other so that each specific crystal axis of them substantially coincide with a polarization transmission axis of polarized light to be transmitted.
In this case, preferably, the liquid crystal panel further includes pixels which are arranged in a matrix on the first sapphire substrate so as to be aligned with a specific crystal axis direction of the first sapphire substrate, a vertical scanning circuit and a horizontal scanning circuit which are formed with the use of a thin film transistor comprised of silicon made by epitaxial growth on the first sapphire substrate, and send a video signal to the pixels, and a transparent electrode formed on the second sapphire substrate.
Preferably, the pixels are arranged in a matrix so as to be substantially parallel with or perpendicular to the specific crystal axis direction of the first sapphire substrate.
Preferably, the first and second sapphire substrates are constructed in a manner that an angle made by each specific crystal axis of them and a polarization transmission axis of a polarized light to be transmitted is set within a range of xc2x12xc2x0.
Each specific crystal axis of the first and second sapphire substrates may be an A-axis or C-axis projection line direction in the case where its primary plane is an R-plane, may be a C-axis or M-axis direction in the case where its primary plane is an A-plane, may be C-axis or A-axis direction in the case where its primary plane is an M-plane, and may be an A-axis or M-axis direction in the case where its primary plane is a C-plane.
The liquid crystal panel has a structure in which the polarizers are arranged on both sides of the panel so that their polarizing directions cross at right angle, and a liquid crystal layer is interposed between the polarizers. When an electric field is an on state, a liquid crystal stands up. In the case where the electric field is an off state, on the other hand, the liquid crystal is twisted. By making use of this charcteristic, the liquid crystal performs a function as a switch for shielding or transmitting light. Therefore, an image can be formed by carrying out an on/off control of electric field for each pixel.
The specific axis orientation of the sapphire substrate is made coincident with an arrangement direction of the pixels and the polarizing direction of the polarized light to be transmitted, whereby it is possible to prevent the sapphire substrate from giving an influence to a polarizing characteristic. Whereby it is possible to realize a high-luminance and small-size liquid crystal projector which is excellent in a heat radiating effect without causing a problem of characteristic deterioration by a heat generation.
Moreover, the specific axis and crystal orientation of the sapphire substrate is controlled as described above, and thereby, it is possible to faithfully maintain a polarizing characteristic, and to realize a liquid crystal projector which can project an image.
Moreover, the pixels arranging on the sapphire substrate in a matrix, and the vertical and horizontal scanning circuits are formed of SOS (silicon on sapphire) thin film transistors, and thus, an active matrix type liquid crystal display device is constructed, thereby making it possible to increase an operating speed and to reduce a power consumption. In addition, since an ordinary semiconductor process can be employed, mass production is possible and, therefore, it is possible to realize a liquid crystal display device having various effects.
In the above embodiments, it is preferable that antireflection coating is subjected onto a surface of the sapphire substrate. Whereby it is possible to improve the transmittance.
The above and further objects, features and effects of the invention will becomes apparent from the following detailed description with reference to the accompanying drawings.